Web guide control



May 21, 1963 J. c. FROMMER ETAL 3,090,534

WEB GUIDE CONTROL Filed March 24, 1959 2 Sheets-Sheet 1 HYDRAULK. PUMP92108 ow"; Ij e p Lia-074mg y 1963 J. c. FROMMER ETAL 3,090,534

WEB GUIDE CONTROL 2 Sheets-Sheet 2 Filed March 24, 1959 a Maya 3,090,534WEB GUmE CONTROL Joseph C. Frommer, Cincinnati, Ohio, and Ulrich R.

Furst, Bellevue, Wash, assignors to Electric Eye Equipment Co.,Danville, 1H,, a corporation of Delaware Filed Mar. 24, 1959, Ser. No.801,503 20 Claims. (Cl. 226-211) This invention relates generally to thecontrol of moving fiem'ble webs and more particularly is concerned withmeans for continually and automatically maintaining lateral position ofa flexible web as it passes through a structure such as a machine whichoperates upon the web.

The invention will be described in connection with apparatus such as amulti-color high-speed printing press having a continuous paper webpassing through the press to be printed in perfect registration, but isnot limited to this application, since the invention is applicable aswell to any machine which requires a flexible web to pass through thesame properly centered with respect to the driving and guiding meansthereof.

The invention is especially intended for use with a structure known as asteering roll, such as that described and claimed in a co-pendingapplication which is owned by the assigned hereof, and entitled SteeringRoll Construction Serial No. 718,057 filed February 27, 1958 by Carl L.Deeken, now Patent No. 2,940,752. The invention herein is directedespecially to the control means per se by means of which the web ismaintained in centered position at all time, and as well to a system ofa type which has been provided to take the maximum of advantage of thevarious components thereof for fast and immediate correction ofdepartures from proper centering.

In any machine in which a web must pass through the same properlycentered, the purposes for which the machine is intended are defeated ifthe web is permitted to wander at will over the various rollers and pastthe various stations of the machine where operations are performedthereon. Only a perfect roll of the material from which the web is madewill travel truly, and this cannot occur unless it passes through aperfect machine. There are so many factors which contribute to the webscreeping to one side or the other of center that a complete catalogherein would be impractical, although several such factors can be namedas illustrative. Some factors are variations in thickness of the web,variations in width of the web, in consistency of ink, variations of theimpression, changes in humidity, variations in mechanical alignment andchanges of temperature.

Several solutions for the problem involved have been proposed and indeedplaced in operation, 'but none of these are to any degree as efiicaciousor sensitive and efficient as the invention herein. Many structuresprovided for lateral movement of the white roll, the stand which carriesthe supply of paper for the press. This requires considerable energy andis only capable of application at one end of the reach of the web; canonly be done slowly because of the great inertia and weight of the whiteroll and stand; and provides sluggish and coarse control only. Othermethods have utilized mechanical guides which attempt to guide the webitself, and in one instance means are provided for keeping the webcentered through the use of pneumatic scanners moving inward and outwardof the center of the web in response to the covering and uncover ing ofopenings in the scanner changing pneumatic pressures. This structure isshown and described in US. Patent 2,666,639, owned by the assignee ofthis application. Inertia problems of this apparatus did not prevent itsbecoming commercially successful, because it operated satisfactorilycompared with the state of the art at the time of its inception, butgreater control and the need for 3,090,534 Patented May 21, 1953 icespeedier response make the present invention a substantial improvementand patentable advance thereover.

The objects of the invention are the provision of a novel and improvedweb guide control for laterally positioning and guiding the web of ahigh speed machine, which is greatly simplified and more efiicient andeconomical than the prior structures.

An important object of the invention is concerned with the provision ofa web guide control that will maintain the web centered on the rolls ofa machine, irrespective of the changes in width of the web.

In connection with this latter object it is pointed out that most of theprior art structures, with the exception of such structures as those ofsaid Patent 2,666,639, operated upon one edge of the Web. The assumptionthat the width of the web is constant is a hope rather than a reality,because the opposite is most usually true, especially with very wideWebs. The change of width of the web as it passes through the apparatusoperating thereon will also change the position of the web it it isguided from one edge and this materially reduces, if not completelyeliminating, the centering control.

The invention herein is primarily concerned with structures in whichcenter line guiding and control is achieved irrespective of the changein width of the web, but in particular instances where single edgeguiding is satisfactory, certain phases of the invention are applicableto single edge control of the web.

Many objects and advantages of the invention can only be appreciated andunderstood through a careful persusal and evaluation of thespecification which follows in which a preferred embodiment of theinvention is described in detail and illustrated in the drawings, albeitsaid drawings are diagrammatic in their appearance.

In said drawings:

KG. 1 illustrates the esesntial components of a system using theinvention for center line guiding of a web passing through a press.

FIG. 2 is a circuit diagram of the electrical control portion of thestructure of FIG. 1 including the two scanners and the amplifier.

FIG. 3 is a circuit diagram of an advantageously modified portion of thecircuit of FIG. 2 in accordance with the invention.

The invention is directed to several phases which are concerned with thefollowing: (1) a system for assuring continuous perfect centering andguidance of the high speed web while passing through a machine; (2) acontrol apparatus used in a system of this kind and which is activatedby means of a pair of scanners providing a pair of signals forcomparison; (3) a system as described in which the control apparatususes only one scanner and has a constant signal simulating a secondscanner against which the first signal is compared to elfect center lineguiding based upon the position of only one edge of the web.

As explained in said copending application Serial No. 718,067, now Pat.No. 2,940,752, it has been found that the maximum control of movement ofa web passing through a machine such as a printing press is achievedthrough the use of a steering roll which is carefully balanced to pivotin a limited plane with a minimum of friction upon an axis which isperpendicular to the axis of the roll and spaced therefrom. Theinvention herein as embodied in the system depends upon this structurefor achieving the unusual and exceedingly high degree of control that isobtained. This steering roll structure is combined with a hydrauliccylinder and a hydraulic system operating the cylinder which iscontrolled by means of a highly sensitive electromagnetically controlledhydraulic differential valve. The particular valve with whichconsiderable success has been had is one which is available commerciallyas a Cadillac valve and can be obtained from Cadillac Gauge. Company ofDetroit, Michigan. This valve has at least two electromagnetic windingsthe flow of current through which provides control of the hydraulicfluid pressure applied to one end or the other of the cylinder. Theamplifier or comparison device of the invention applies current throughthe two windings to vary the position of the cylinder and hence pivotthe steering roll until the signals from the scanners are equal, atwhich time there will be no further movement of the steering roll.

In the case of the single edge guide, instead of two scanners a signalis obtained from a fixed source and the signal from a single scanner iscontinuously compared with this to provide the currents in the windingsof the sensitive electrically energized hydraulic valve.

Considering now the illustrations, in FIG. 1 there is 7 shown a portionof a press which has a web of paper passing through the same. The web isdesignated 10 and the arrows show the direction of movement thereof. Theweb 10 passes over a steering roll 12 with the incoming reach and theoutgoing reach substantially parallel one with the other, an arrangementwhich has been found most effective and sensitive for steering rollcontrol. The steering roll 12 rotates on an axis 14 which issubstantially horizontal and is journalled at the ends 16 of arelatively rigid elongate yoke 18 which is pivotally mounted upon apivot assemblage 20 suitably secured upon the framework 22 or base ofthe press. The axis 24 of the pivot assemblage 2G is perpendicular tothe axis 14 and is spaced therefrom as indicated by the arrow 26.

The right hand end 16 of the yoke 18 has a pair of cars 28 providing thepivotal journal for the eye 30 formed on the end of the piston rod 32 ofa hydraulic cylinder 34 the opposite end of which is pivotally securedat 36 to a part 38 of the framework of the press. Adjustment of thepressure of the hydraulic fluid applied to the cylinder 34 through itsend ports 40 and 42 by means of the hydraulic pump 44 operating throughthe sensitive magnetically controlled valve 46 will swing the yoke 18one way or the other about the axis 24. The control currents in thevalve 46 are provided from the amplifier 48 by way of electricalconnections designated generally 50.

The amplifier 48 is a comparison device, which electronically andcontinuously compares signals obtained from the two scanners 52 and 54on the outgoing reach of the web 10. These two scanners are of a basicform well-known, comprising photo-sensitive devices such asphotoelectric cells activated by projected light from suitable sourcessuch as indicated at 56 and 58. The optical components of these systemsare too well-known to require description, but insofar as theapplication herein is concerned, a narrow slit of light is permitted toimpinge against each of the photo-sensitive devices, as for examplethrough the transparent windows diagrammatically indicated at 60 and 62.This narrow slit is intercepted by the edge of the web to decrease orincrease the amount of light that the respective scanners receive andhence to vary the amplitude of signals provided thereby and applied tothe comparison device 48. Since the valve 46 will continuously changethe amount of the piston rod 32 that protrudes until the amplitudes ofthe signals applied to the comparison device 48 are equal, the web 16will continuously seek the precise center of the distance between thetwo scanners 52 and 54 (which are of course adjusted to be equallyspaced on opposite sides of the centerline that it is desired the webshould follow).

It will be appreciated that for the structure described, the amplitudesof signals from the scanners 52 and 54 will not necesarily remainconstant for the condition of perfect centering, although the signalamplitudes will be equal with respect to one another for perfectcentering. This means that the width of the web may vary withoutaffecting the centering of the web, since this is automaticallycompensated for by the system. Likewise, the fogging of the opticalsystems of the scanners will have no effect upon centering since bothwill usually fog the same amount over the same period of time.

The system may be varied by eliminating one or the other of the scanners52 or 54 and providing a source of constant potential in its placeagainst which the signal from the remaining scanner may be compared.This system will not be as effective as that which continuouslymaintains centering irrespective of the web Width, but is superior toother known structures using one side edge of the web for guidingcontrol.

Such an advantageous detailed modification of the control circuits, tobe seen hereafter in connection with the discussion of FIG. 2, isillustrated in FIG. 3. The utility and function of this circuit of FIG.3 becomes more clear by considering the succeeding description of 'FIG.2. For the moment, however, in FIG. 3 there is shown an arrangement forsubstitution in the circuit of FIG. 2 upon eliminating one of the abovenoted scanners 52 or 54. Associated circuit elements of FIG. 2 aresimilarly positioned and numbered in FIG. 3 for illustrating theadaptation of these modifying circuits of the latter FIG. 3 to the moregeneral apparatus of FIG. 2;

In this FIG. 3 a control grid of the double triode tube V1 is connectedby way of lead 88 to the variable contact of a potentiometer 155. Thefixed contacts of this potentiometer, as shown, connect thispotentiometer across a source of potential indicated by B+ and a groundsymbol.

Thus the bias potential of one control grid 88 of tube V-l is manuallyadjustable by the potentiometer. As will be seen hereafter, this grid 88is connected, in another embodiment of the invention, to the cathodeelectrode of a photoelectric tube, such as tube V-S, for application ofgrid potentials under control of light rather than under resistorcontrol by a potentiometer.

Referring now to FIG. 2 the DC. amplifier or comparison means 48 isshown in a detailed circuit diagram along with other components of thesystem. The sources of light are shown as lamps at 56 and 58 directingtheir light through suitable optical trains past the respective edges ofthe web 10 through slits 60 and 62 respectively of the scanners 52 and54. Each scanner has a photoelectric tube as at V5 and V-6, oneelectrode of each being connected to the B+ supply conductor 74 and theother electrode of each being connected to the scanner signal balancingmeans indicated generally at 76. The negative electrode of tube V5 isconnected through the resistor R201 in lead 78 through the high ohmagevariable resistor R311B to the common conductor of the section C of thefour-pole five-position switch 80. The negative electrode of the tubeV-6 is connected through the resistor R201 in lead 82 through the highohmage variable resistor R311A to thelead 84, one end of which connectswith all four of the first four contacts of section C of switch and theother end of which connects through a voltage divider 86 to ground.

During operation, the wipers of the variable resistors R311A and R311Bare adjusted in unison to give equal signal output from tubes V-5 andV-6 for equal amounts of intercepted light.

Flow of current through the resistors R201 produces D.C. potentials atthe grids 88 and 90 of the left hand sections of the tubes V-l and V-2.The plates 92 and 94 of the sections of each tube are connected togetheras shown so that the tubes each have single output circuits, and thepotential thereof applied respectively by way of the leads 96 and 98 andresistors R107 and R109 ot the respective grids 160 and 102 of tube V-3.Cathodes 104 of the tube V1 are connected together and extend by thelead 186 to a source of negative potential 108 through resistor R112.Cathodes 110 are also connected together and extend by way of lead 112through a similar resistor R116 to the same source of negative potential198. The grid 88 is connected through the resistor R202 to the grid 114and the grid 90 is connected through a similar resistor R202 to the grid116.

The resistors R108 and R110 are voltage dropping resistors for theplates 92 and 94 respectively being connected to the B+ supply line 74.The plates 118 and 120 of tube V3 are connected in parallel with theplates 122 and 124 respectively of the tube V4 so that the plate currentof both tubes flows through the respective windings 126 and 128 of thevalve 46 through the common conductor 130 to the B+ supply line 74through the dropping resistor R102. The grids 100 and 102 arerespectively connected to the grids 134 and 132 of tube V4 throughresistors R105 and R104. All of the cathodes 136 and 138 of the tubesV-3 and V4 are C0114 nected to the negative potential source 108 throughthe resistor R103. The left hand cathodes and right hand cathodes eachhave a degeneration resistor R106 sepa-. rating same from resistor R103.

The resistors R202, R104 and R105 keep the grids on opposite sidesthereof at equal potential and prevent unwanted parasitics, and hence itmay be considered that both sections of tube V-1 act as one tube, bothsections of V2 act as one tube, the both left hand sections of tubes V3and V4 act as one tube, and both right hand sections of tubes V-3 and V4act as one tube. Indeed, the basic invention may be considered asutilizing a total of four single section tubes or two double sectiontubes, not counting the photo-tubes.

The tubes V-l and V-2 receive D.C. signals which are amplified andapplied to the right and left sections of the tubes V3 and V4respectively resulting in an output current flowing through the windings126 and 128 which will result in no change in the pressure at oppositeends of the cylinder 34 if the currents are equal, but which willunbalance if the currents are not equal and cause the servo effect tobring the web back to center. Note that changes in line voltage, widthof web, fogging of optical systems, and any variation that occurs toboth of the scanners 52 in like amount will have no effect upon control.

The amplifier circuit 48 is unusual in that it provides variablesensitivity to the differential between the signals appearing at thegrids of the respective tubes V1 and V2, that is, when the scannersignals are not equal; and it provides maximum of degeneration and hencelow sensitivity and high stability when the signals are of substantially equal amplitude.

The desideratum when equal level signals occur is to keep rated currentflowing in the windings 126 and 128 of the valve 46. When signals ofdifferent level occur, their difference is to be emphasized so that aspeedy and immediate response will be made to bring the web back tocentered position.

The plate load resistance R108 and R110 of the respective tubes V1 andV2 is chosen to be approximately half of the cathode resistance R112 andR116. In the actual circuit this ratio was 150,000/ 330,000. Equalsignals would therefore be reduced by a factor of one-half. Consideringcathode follower action, since the signals on the cathodes and grids ofthe respective tubes V-l and V2 are substantially the same, the currentflow through the resistor R108 and resistor R112 will be the same. Thesignal across the plate resistor R108 will however be half that of thesignal across the cathode resistor R112. This is also true for the tubeV2 and its plate and cathode resistors R110 and R116, respectively.

Note that there is a value of resistance between the two cathodes 104and 110 which may be represented by the broken line equivalent resistorR This resistance R is determined by the following circuitry: the lead106 connects with the wiper 140 of the multi-position switch 142connected as a variable resistance element by the lead 144 directly tothe cathode 110 through contact No. 5 of the section D of switch 80 andthe switch wiper (position 5 of switch 80 is OPERATE) and the lead 6112; a parallel connection is by way of lead 146 from the lead 106through resistor R306 and resistor R302 to lead 112. These latter tworesistance paths are in parallel. The sensitivity of the compensatingeffect of the amplifier 48 is controlled by the position of the wiper140 of the switch 142.

The value of this resistance R the equivalent of the two parallel pathsdescribed, is immaterial if the flow of current through the tubes V-1and V2 is of the same D.C. level. It could be either zero or infinitefor inphase signals.

Now we consider what happens if the signals on the two tubes V-l and V2are not the same and the currents flowing through these tubes aredifferent, related in value to the amount of light lost by one scannerand gained by the other. If R were infinite, then the two tubes Vl andV2 would act in the same manner that they acted when equal D.C. levelsignals were received, namely, all signals are decreased in their outputcircuits. This would give an error differential it is true, but onewhich is of low sensitivity due to the halving of signals, because ofcathode degeneration.

If the tube cathodes 104 and 110 were connected in short circuit, thesignals at the grids 88, 114 and 90, 116 would have to change thecathode currents of the tubes in opposite directions in order tomaintain the same voltages on both cathodes (recalling that one set ofgrids is receiving a high voltage and the other set of grids isreceiving a low voltage) since the cathodes are connected together.There can thus be no cathode follower action or degeneration in thetubes, and all of the signal of each tube will appear at its respectiveplate with one being substantially greater than the other, to a muchgreater degree than the difference between the signals that caused theflow of current. The full amplification of the tubes Vl and V2 comesinto effect, and the signals applied to the output tubes V3 and V4 areaccordingly of much greater differential. This increases the sensitivityof the device.

Instead of having R as a short circuit, which is of course feasible insome installations, it is adjustable, to thereby control the sensitivityof the apparatus.

The necessary power for the amplifier 48, and if desired for thefilaments of the lamps 56 and 58, can be obtained from power sourcesthat may be associated with other electrically operated apparatus usedin connection with the structure of the invention. In the circuitdiagram there is illustrated a suitable power supply which is comprisedof a full-wave rectifier tube V-7 having the high voltage secondarywinding 162 of a transformer 160 connected across its plates. Thetransformer primary winding 161 is connected across the power line. Thenegative potential for the lead 108 is obtained from a center tap 163 ofthe secondary winding 162 connected to the lead 108 at the point 165. Itwill be noted that this point is at a negative potential because thepoint 167 between the resistors R114 and R is at ground potential. Theresistor R101 is a voltage dropping and filter resistor and provides ahigh B+ potential of 260 volts DC. at the point 169. It is shunted tothe point 165 by means of the filter condenser C The resistor R102 alsodrops the voltage of the point 171 to volts DC. and is shunted to pointby filter condenser C The filament secondary 174 is connected across thecathode of the tube V7, and there may be additional filament secondariesfor other tubes in the apparatus. In the actual device the filaments ofthe lamps 56 and 58 were energized from a separate transformer and eachfilament had a variable resistor in series wherewith to adjust itsbrilliance, but it is not believed necessary to illustrate this since itis a well known arrangement.

As previously stated, the various pairs of tubes act in effect as singletubes, but are used for reliability. Efiort must be taken to prevent thedifferences between the characteristics of the tubes from affecting theoperaconnected directly to the meter M3tl1.

tion of the device. In the case of the outpu tubes V3 and V-4 it hasbeen found that the connection of the low ohrnage resistors R106 to thepairs of cathodes provides some cathode degeneration in the respectivesections of the tubes. In this manner the equality of the currentsflowing in the coils 126 and 128 of the sensitive valve 46 will be lessdependent upon the equality of the characteristics of the sections ofthe tubes V-3 and V-4.

These two low ohmage resistors Rltifi are respectively associated withdual current paths to coils 126 and 128. The two resistors are togetherconnected in series with a relatively large resistor RitB in the cathodecircuits of dual tubes V-3 and V-4. These three resistors all make fordegeneration of signal currents passing through the plate circuits ofthe two tubes. The relatively small size of resistors Riitfi makes theoverall degeneration effect of these two resistors small in comparisonto the degenerative effect of the large resistor 103.

Now, by reference to the drawing FIG. 2, it is seen that those platecurrents of double tubes 1-3, and V-4 which are associated with each ofthese two small resistors R196, flow to different ones of the controlcoils 126 and 128. Both these coil currents, however, are degenerativelyaffected by current flow in the large common resistor R193. What is theeffect of this division of currents and the relative sizes of theseresistors? As a large current tends to flow through either or both coils126 and 128 under the'infiuence of light controlled signals from tubesV5 and V6, these large signals are both degenerated by the commoncathode resistor R103. But the differential of signals flowing throughthe respective resistors R106 is not correspondingly degenerated. Thisfollows since resistors R106 are substantially smaller, by an order ofmagnitude, than common resistor R103.

Accordingly, the overall signal applied to these coils by a large changein light at tubes V-S and V-6 results in a correspondingly degeneratedchange in overall signal at the coils 126 and 123. But a very muchsmaller factor of degeneration is applied to the differential signalbetween the two coils.

As a net result, the overall sensitivity of the coil controlling systemis inhibited against overlarge increase and possible physical damage tomoving parts. At the same time this inhibiting reduces the systemsensitivity to selective operation by valve 46 by only a relativelysmall amount.

It has been found that the amplifier described above working inconjunction with the components described gives excellent and reliablecontrol. p

In the circuit of FIG. 2 some of the components have ,not been describedin detail, and these need not be explained since their purposes andoperation should be obvious. The switch 8% is for testing and adjustingthe circuit. All of the wipers are ganged as at 180. The variouspositions may be briefly explained hereinafter without the need fortracing the circuits:

Position 1 shown.

Position 2 In this position the cathode 104 is connected through meterM591 through a. multiplier and cathode 110 is The series con- "8 nectionof metersM301 and M501 is through the multiplier resistor R305 betweencathodes 104 and 110 so that if the voltage at both cathodes is equal,no voltage drop occurs across the meters and resistor R305. However, ifcathode 104 is at one potential and cathode 110 at another potential,the meters both indicate the direction and magnitude of the difference.This gives the difference between the two to enable the balancing of thescanners through the balance 76. Note that in this position as in allothers but position 5, the input tubes are connected as pure cathodefollowers and the low ends of the cathode balance resistors R311-A andR311-B are connected together and to a fixed point between resistorsR401 and R402. 1

Position 3 In this position again the cathode voltage of tube V-l iscompared against a fixed voltage to enable physical adjustment of thescanner 52 so that exactly half of the light will fall on that scanner.

Position 4 In this position, the cathode voltage of tube V-2 is comparedagainst a fixed voltage to enable physical adjustment of the scanner 54.

Position 5 This is the operating position. When the switch is placed inthis position the averages of the voltages of the two cathodes are againbeing compared at all times. In section B, however, there is a differentvoltage due to the connecting of other components in its circuit. Avariable voltage may now be applied by movement of the fine control ofresistor R404 to simulate physical movement of the scanner 52 for fineadjustments of the scanners. This position also connects the sensitivitycontrol into the circuit.

The first stage of the amplifier, namely the tubes V1 and V-2 areusually located in the same housing as the respective photocells of thescanners.

Note that the cathodes 136 and which are slightly higher than the gridsof the respective sections of the tubes V-3 and V-4 so that there isalways a certain value of current flowing in the windings of the valve46 as required for most efficient operation thereof. a

The operation of the structure with a fixed voltage applied instead of asignal from one of the scanners is no different than described. Therewill be a greater difference between the response of the amplifier(i.e., its output) to the signals of different D.C. level than thedifference between the signals themselves; while the response atconditions of equal level signals will be relatively smaller, and henceless sensitive. This of course is characteristic of the structure whentwo scanners are furnishing the signals, but the difference between theresponse of the equal and unequal signals for the two scannerarrangement is even more marked. This is because as one scanner signalbecomes greater the other becomes smaller, and vice versa.

In viewing the overall character of the device, it may be consideredthat the circuit provides cathode degeneration in the stages atconditions when the respective signals from the scanners aresubstantially equal and no degeneration when the signals are not equal,thereby enabling the maximum of amplification of the tubes to beavailable, for the difference. Stating this in another way, since theamplifiers areresponsive to a DC. voltage produced by the respectivescanners, the average level of voltage affects the output very little,but the difference between the levels has a very substantial effect.

The construction of a practical embodiment of the invention should beapparentto those skilled in this art,

138 are at voltages be set forth hereinafter:

RESISTORS (in ohms) 2K. (K thousands) 33K.

10 nieg. pct. -10 meg. pot.

A meg. R404 20K. pot. Switch 1'42 Resistance between points to give widerange of sensitivity, from 4.7 K ohms between points 10 and 11, to 330Kohms between points 2 and 3. Total resistagce approximately 665K ms.

M301, M401, M501-" Microam meters.

C-l, 15 mfd. filter condensers.

V-1, V2 12AX7 vacuum tubes.

V3 ,V4 12AT7 vacuum tubes.

V-5, V6 CE34Q photoelectric tubes.

V-7 Y3 rectifier tube.

As stated above, the invention is applicable to a wide variety ofapparatus in which a moving web is to be steered to maintain itscentering, either with respect to a centerline of the web, or relativeto one edge. Considerable changes may be made without departing from thespirit or scope of the invention as defined in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

l. A system for guiding a flexible web through a machine which operatesupon the web, and which includes a steering roll mounted for rotation ona first axis transverse of the web and for pivotal swinging on a secondaxis perpendicular to said first ax-is but spaced therefrom on the sideof the oncoming reach of said web, a pair of illuminating means on theoutgoing reach of said web, one on each edge thereof and photo-sensitivesignal producing means at each edge receiving a defined beam from saidilluminating means and the web adapted to intercept an equal portion ofeach beam to produce an equal signal output from each signal producingmeans when said web is substantially centered between said signalproducing means, an electronic comparison means connected to receivesaid signals and arranged to provide an output which is amplified to agreater extent for one difference between the signal outputs of saidsignal pro- 'ducing means than at another difference between the signaloutputs of said signal producing means, an electromagnetic hydyrauliccontrol valve receiving said differential output, and hydraulicactuating means connected with said steering roll to swing same aboutsaid second axis and controlled by said control valve to pivot saidsteering roll in a direction for shifting said web laterally to maintainequal signal outputs.

2. A system as claimed in claim 1 in which said comparison meanscomprise an amplifier having a pair of signal channels includingelectronic amplifier states having low amplification when said signalsare equal and high amplification when said signals are unequal.

3. A system as claimed in claim -1 in which said comparison meanscomprise a pair of electronic amplifier roll mounted for offset swingingand having a hydraulic actuator for swinging same, a hydraulic systemfor driving the actuator and controlling the same including anelectromagnetic valve including a pair of difierential windings, ascanner on at least one edge of said web on the outgoing reach relativeto said steering roll and having illuminating means and aphoto-sensitive signal producing means thereat arranged to receive abeam from said illuminating means with the web at least partiallyintercepting said beam to control the signal from said scanner, a secondsignal-producing means responsive to another beam which is interceptedto a degree determined by the position of said web, and a comparisoncircuit receiving the signals from both means and providing a pair ofoutput currents related to one another in a non-linear manner dependingupon the difierence between the signals from the photosensitiveproducing means and the second signal producing means, said differentialwindings being against which said signal from said photosensitive signalproducing means may be compared to guide said web from the position ofsaid one edge thereof.

6. A system as claimed in claim 4 in which there is a second scanner andilluminating means on the opposite edge of said web, and said secondsignal-producing means is also photo-sensitive and receives a beam fromsaid second illuminating means and the web also at least partiallyintercepts said beam to control the signal from said second scanner, andthe signals from both are compared to guide said web from the geometriccenter between said scanners.

7. In a system in which a web is steered to keep same centered as itpasses through a machine having scanners Y scanning the edges of theweb, a comparison amplifier for comparing signals from said scanners andproviding difierential current outputs which includes a pair of signalchannels each having at least a cathode follower stage with the cathodesconnected together, and a pair of Y amplifier stages driven respectivelyby the cathode folinstance, and the output circuits of said amplifierstages having said current outputs flowing therein.

8. In a device of the character described in which a moving webintercepts light directed at a pair of scanners and means are providedresponsive to the signals from I said scanners to maintain the webcentered by movement of a steering roll through a control system, anelectronic circuit for comparing said signals to provide a pair ofoutput signals whose relative values are related to the difference ifany between the signals from said scanners, said circuit including apair of cathode follower stages each connected with an amplifier stage,and the output signals adapted to appear in the output circuits of saidrespective amplifier stages, the cathode follower stages each includingan electronic tube including a cathode and the cathodes each connectedfor providing degeneration in the respective cathode follower stage whenthe scanner signals applied thereto are equal but no degeneration whenthe scanner signals are unequal whereby the unequal signals will beamplified in said cathode follower stages and said electronic circuitwill have greater sensitivity for unequal scanner signals.

"9. A structure as claimed in claim 8 in which adjustable resistancemeans is connected between said cathodes to vary the sensitivity of saidelectronic circuit.

10. A structure as claimed in claim 8 in which a constant signal isprovided in place of a signal from one of said scanners and the otherscanner is located adjacent one edge of said web and its signal varieswith respect to the position of the web relative thereto.

11. A structure as claimed in claim 8 in which said scanners are locatedon opposite edges of said web and the signals therefrom vary with thelaterial disposition of said Web and in opposition one to the other.

' 12. In a system for guiding a moving Web of material into locus on amachine wherein a member performs work on the web, means for maintainingproper alignment of the web with said member, said means comprising thecombination of means for shifting the position of the web in eitherdirection transverse to its line of travel into said locus, edgescanning means for the web operated responsive to the deviation of saidweb from said proper "alignment and deriving electrical signalsproportional to said deviations, difierential amplifier means connectedto receive said signals and responsive thereto to derive an amplifiedelectrical output indicative of the direction and proportional to theextent of said deviations, a bidirectional hydraulic mover connected tosaid web shifting means to motivate the same, a source of hydraulicfluid for actuating said mover, an electrically actuated flow regulatingvalve through which fluid from such source is transmitted to said moverto operate the latter in the direction selected, said valve beingconnected to receive said output from the amplifier and being responsivethereto to select said direction and determine the rate at which fluidis supplied to said mover, the system being further characterized inthat, by virtue of the construction, arrangement and inter-connection ofthe elements of said combination, said web shifting means is moved in adirection to correct said deviations and at a rate which variesproportionally with the extent of the instantaneous web deviation fromsaid proper alignment.

13. The system of claim 12 wherein said scanning means comprises a lightsource, two photo-sensitive elements and light masking means for thelatter disposed adjacent a respective edge of the web, one of saidphotosensitive elements providing an electrical signal having apotential which serves as a reference in said amplifier and the otherphoto-sensitive element providing signals to the amplifier which have apotential varying proportionally with the extent of said deviations andwhich 'are of positive or negative value with respect to said referencesignal dependent upon the direction of the deviation.

14. The system of claim 12 wherein said scanning means comprises a lightsource, a photo-sensitive element and making means for the. latterdisposed adjacent opposite edges of the web, each of saidphoto-sensitive elements providing electrical signals to said amplifierhaving a. potential which varies proportionally with the extent of theweb deviation detected by that element, the instantaneous signal fromone of said elements providing a reference potential in saiddifferential amplifier and the instantaneous signal from the otherelement being of positive or negative value with respect to the saidreference signal dependent upon the direction of the deviation at oneedge of the web as compared to that at its opposite edge.

15. In a system for guiding a moving web of material into a locus on amachine wherein a member performs work on the web, and in which theproper alignment of the web with said member must be maintained, thecombination comprising means for shifting the position of the web ineither direction transverse to its line of travel into said locus,scanning means disposed adjacent at least one edge of the web, saidscanning means having photo-sensitive means responsive to deviations inthe I web from said desired alignment and driving electrical 'errorsignals the potential of which varies proportionally 'said referencesignal and responsive thereto to derive an amplified output varying inpositive and negative value, with respect to said reference signal,dependent upon the direction of said deviation and having a magnitude,with respect to said reference signal, which varies proportionally withthe extent of said deviation, a bidirectional hydraulic mover connectedto said web shifting means to motivate the same, a source of hydraulicfluid for actuating said mover, an electrically actuated flow regulatingvalve through which fluid from said source is transmitted to said moverto operate the latter in the direction selected, said valve beingconnected to receive said output from the amplifier and being responsivethereto to select said direction and determine the rate at which fluidis supplied to said mover, the system being further characterized inthat, by virtue of the construction, arrangement and interconnection ofthe elements of said combination, said web shifting means is moved in adirection to correct said deviations and at a rate which variesproportionally with the extent of the instantaneous web deviation fromsaid proper alignment.

16. In a system for guiding a moving Web of material into a locus on amachine wherein a member performs work on the web, and in which theproper alignment of the web with said member must be maintained, thecombination comprising means for shifting the position of the web ineither direction transverse to its line of travel into said locus,scanning means disposed adjacent each of the opposite edges of the web,each scanning means having a photo-sensitive element responsive todeviations in the position of the corresponding edge of the web and eachphoto-sensitive element providing electrical signals the potential ofwhich varies with the extent of the deviation detected by that element,a differential amplifier connected to receive said signals from each ofthe scanning means and responsive thereto to provide an amplified outputhaving a potential proportional to the difference in potential betweenthe signals from the individual scanning means, a bi-directionalhydraulic mover connected to said web shifting means to motivate thesame, a source of hydraulic fluid for actuating said mover, and anelectrically actuated fiow regulating valve through which fluid fromsaid source is transmitted to said mover to operate the latter in thedirection selected, said valve being connected to receive said outputfrom the amplifier and being responsive thereto to select said directionand determine the rate at which fluid is supplied to said mover, thesystem being further characterized in that, by virtue of theconstruction, arrangement and interconnection of the elements of saidcombination, said web shifting means is moved in a direction to correctsaid deviations and at a rate proportional to the extent of deviationsof the longitudinal centerline of the web from its desired alignmentwith said work performing member.

17. In a web scanning system wherein two portions of a moving web arescanned for the purpose of providing a pair of electrical signals therespective amplitude of which is dependent upon the lateral pisition ofeach portion with respect to the direction of web movement, in whichthere is a web-adjusting device acting laterally on the web and drivemeans for operating the web-adjusting device, and in which there is adilferential signal comparator having its output connected to the drivemeans, the improvement comprising: a pair of parallel amplifiers eachdriven by a respective one of said signals and providing an amplifiedoutput signal corresponding to the respective input signals received,feedback means connected between said amplifiers providing a variabledegree of amplification of said amplifiers the value of which is relateddirectly to the difference between the amplitudes of said electricalsignals, whereby for a small difference in signal input amplitudes thedegree of amplification will be low, whereas for large difierences insignal input the degree of amplification will be high, the outputsignals being connected to said differential signal comparator wherebythe degree of adjustment of the Web laterally depends upon the degree ofamplification of said amplifiers and hence upon the difierence inamplitude between said input signals.

18. The arrangement claimed in claim 17 in which each of said amplifiersis provided with a grid circuit at which the respective signal isreceived and said feedback means includes a feedback circuit connectedbetween the grid circuits.

19. The arrangement claimed in claim 17 in which said feedback meanscomprise, first cathode resistor means common to said amplifiers andsecond cathode resistor means individual to each of said amplifiersconnected to one side of said common resistor means.

20. In a system of the character described in which a flexible Webpasses over a steering roll in a machine which operates upon said web,and in which means are provided for swinging the web including anactuating device operated by a pair of amplifier output signals Whoserelative values determine the extent of actuation; comparison meansdriven by a pair of input signals at least one of which is related tothe position of an edge of said web to produce said output signals,comprising a pair of electronic amplifier stages having connection withone another to provide cathode degeneration in the respective stageaccompanied by low amplification while the stages are receiving saidinput signals and said signals are of substantially the same amplitude,but also eliminating cathode degeneration when the said input signalsare of difierent amplitudes whereby substantially to increase theamplification of said stages and therewith the sensitivity of saidcomparison means to unequal input signals.

References Cited in the file of this patent UNITED STATES PATENTS2,451,816 Dunn Oct. 19, 1948 2,722,415 Wood Nov. 1, 1955 2,840,371Frommer June 24, 1958 2,840,722 Frommer June 24, 1958 2,866,407 Hackelet al. Dec. 30, 1958 2,883,559 Bailey Apr. 21, 1959

7. IN A SYSTEM IN WHICH WEB IS STEERED TO KEEP SAME CENTERED AS ITPASSES THROUGH A MACHINE HAVING SCANNERS SCANNING THE EDGES OF THE WEB,A COMPARISON AMPLIFIER FOR COMPARING SIGNALS FORM SAID SCANNERS ANDPROVIDING DIFFERENTIAL CURRENT OUTPUTS WHICH INCLUDES A PAIR OF SIGNALCHANNELS EACH HAVING AT LEAST A CATHODE FOLLOWER STAGE WITH THE CATHODESCONNECTED TOGETHER, AND A PAIR OF AMPLIFIER STAGES DRIVEN RESPECTIVELYBY THE CATHODE FOLLOWER STAGES, THE CATHODE FOLLOWER STAGES CONNECTEDFOR PROVIDING MAXIMUM DEGENERATION WHEN THE SIGNAL INPUTS